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Thread: 'T' tail verses Conventional layout.

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    'T' tail verses Conventional layout.

    On my short list for my retirement project is, amongst others, the Titan Tornado. Looking at various videos and forum posts the tail feathers get very close to the ground both on take-off rotation and the landing flare. Some damage has been done in some cases, even on fairly smooth, regular surfaces, let alone the potential on a more 'challenging' strip ..... and so my question;

    What are the pro's and con's of going for a 'T' tail design in this situation. Apart from looking good (subjective, I know), it would seem to help eliminate a slight negative factor in the original design.

    What additional factors have to be catered for structuraly and aerodynamicaly in considering such a design ? Even a mid set horizontal stabaliser might be an option.

    Any comments please.

    Regards, David.

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    Registered User etterre's Avatar
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    Re: 'T' tail verses Conventional layout.

    Quote Originally Posted by OzExpat View Post
    ...On my short list for my retirement project is, amongst others, the Titan Tornado. Looking at various videos and forum posts the tail feathers get very close to the ground both on take-off rotation and the landing flare. Some damage has been done in some cases, even on fairly smooth, regular surfaces, let alone the potential on a more 'challenging' strip .....
    Where could I go for more info on the nature of the damage? I'm currently thinking about building a Janowski J1B (pictures can found at www.vula.org ) and it has a tail layout similar to the stock Tornado. I looked at the Yahoo group (Titanaircraft), but it looks like I have to join up to be able to search the messages.

    Thanks!
    Last edited by etterre; February 27th, 2007 at 08:43 AM. Reason: spelling mistake, clarification on tail type

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    Super Moderator orion's Avatar
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    Re: 'T' tail verses Conventional layout.

    The main issue of consideration for "T" tails is simply weight. Horizontal tails must not only deliver the necessary up and down loads, but in order to be safe in all flight conditions, must be able to be loaded so that a sizable torque is created on the mounting structure. This is due to unsymmetrical loadings encountered as a function of gusts, asymmetric flight conditions, etc. In a "T" tail this must be supported by the vertical tail structure, which now has to be stronger and stiffer.

    From a control standpoint, there would be some issues if the tail was in the direct flow off of a pusher prop but in general, for a light aircraft the effect is minimal with the exception that your trim will be a bit different since the horizontal will not see as much downwash off the wing In a high wing there would be less change than with a low wing.
    "To live is to learn; to learn is to live" (author unknown)

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    Re: 'T' tail verses Conventional layout.

    etterre; The damage was to the tail wheels, which in the Titan Tornado is realy only a 'bumper' as it's basicaly a tricycle gear design, but they were damaged or even ripped off due to over-rotation or too much flare resulting in a tail first touchdown. Possible damage to the stabilizer was my worry as it is so low set on this otherwise delightfull design and it would only require an uneven strip plus a bit of mishandling for it to collect something as well. ie. only well manicured strips please.

    orion; Thanks for the feedback. I think I'm straying too far from the 'keep it simple' philosophy, so perhaps I'll just let it go for the time being, as I have no way of determining the correct fixes for the items you pointed out.

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    Re: 'T' tail verses Conventional layout.

    would it be possible to put longer gear legs on it? might be simpler than changing the tail around.

  6. #6
    Super Moderator orion's Avatar
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    Re: 'T' tail verses Conventional layout.

    Looking at some of the pictures, I can see how the horizontal might get damaged. It also seems a hair on the small side however that is really dependent on the type of flap and the size of the allowable CG range you might be after so I'll leave that alone.

    For the given Tornado configuration though, the biggest issue of a "T" or cruciform tail is that it places the surface directly behind the prop. Like with a number of amphibious aircraft where the engine is mounted on top of a pylon, having the surface directly behind the prop will do several things but the first and foremost effect is a substantial trim change as a function of power setting. Descending or coming in to land, where the prop is windmilling, the tail is pretty much blanketed so the first thing you'd have to do is increase the tail area in order to make sure that you maintain sufficient trim and control authority.

    But as you trim for the blanketed tail, doing a go-around or some other maneuver that required you to apply power quickly would result in a sudden increased tail force, which could initiate a maneuver you didn't intend. As such, any such modification would have to be considered in full light of the secondary effects the change would create.
    "To live is to learn; to learn is to live" (author unknown)

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    Re: 'T' tail verses Conventional layout.

    OzExpat [expat from Kansas?]

    Strongly suggest downloading the following publication from FAA AC website, regarding unconventional stabilizers: Evaluation of Flight Loads on Small Airlpanes with T, V, +, or Y Empennage Configurations

    http://www.airweb.faa.gov/Regulatory...ght=stabilizer

    Regards WKT
    Regards, WKT

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    Registered User bmcj's Avatar
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    Re: 'T' tail verses Conventional layout.

    Another concern, although rare, is the possibility of blanketing (blanking?) the horizontal tail in the turbulent wake of the wing (in particular, a low wing configuration) during a deep stall. Learjet encountered this problem and had to add ventral strakes (the two small, angled fins you see on the bottom of the tailcone) to remedy the problem (the strakes are in "clean" air during deep stalls).

    Orion is quite correct about the need for a reinforced vertical tail and about power related trim changes. I have seen a couple of designs that get around the trim change problems by adding a small full flying trim tab down on the tail cone (thus avoiding a trimming surface in the propstream).

    Bruce

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    Re: 'T' tail verses Conventional layout.

    Quote Originally Posted by wktaylor View Post
    OzExpat [expat from Kansas?]

    Strongly suggest downloading the following publication from FAA AC website, regarding unconventional stabilizers: Evaluation of Flight Loads on Small Airlpanes with T, V, +, or Y Empennage Configurations

    http://www.airweb.faa.gov/Regulatory...ght=stabilizer

    Regards WKT
    Hello all. I tried clicking on the link above, but I get a "problem loading page" error.

    Is this just me, or is everyone else having the same problem?

    cheers,
    Brad

  10. #10
    Registered User bmcj's Avatar
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    Re: 'T' tail verses Conventional layout.

    It works for me.

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    Re: 'T' tail verses Conventional layout.

    Folks, try again...

    I was able to click on the link and make it work [sometimes the FAA AC websit "stubs its toe"].

    IF the exact address won't paste properly,then... Go to: http://www.airweb.faa.gov/Regulatory...ryCircular.nsf

    Select: "Web Current AC by Number"

    Find AC23-9 "Evaluation of Flight Loads on Small Airlpanes with T, V, +, or Y Empennage Configurations"

    Also of possible interest: AC23.143-1 "Ice contaminated Tailplane Stall"

    NOTE: There is/are LOTS of great info contained in these downloadable ACs.

    Regards, WKT
    Regards, WKT

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